Shell for mattress



FIG. 1 is a perspective view of a shell for mattress in accordance with the new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a bottom view thereof;

FIG. 6 is a side view thereof; and,

FIG. 7 is a side view thereof. 

CLAIM The ornamental design for a shell for mattress, as shown and described. 